1. Field of the Invention
This invention relates to memory card systems, and more particularly to removable memory card sockets for dual-protocol memory card systems.
2. Related Art
Flash-memory cards are widely used for storing digital pictures captured by digital cameras. One useful format is the Secure-Digital (SD) format, which is an extension of the earlier MultiMediaCard (MMC) format. Such memory cards are also useful as add-on memory cards for other devices, such as portable music players, personal digital assistants (PDAs), and even notebook computers. SD cards are hot-swappable, allowing the user to easily insert and remove SD cards without rebooting or cycling power. Since the SD cards are small, durable, and removable, data files can easily be transported among electronic devices by being copied to an SD card. SD cards are not limited to flash-memory cards, but other applications such as communications transceivers can be implemented as SD cards.
SD and MMC are complementary card interfaces, and are sometimes lumped together and referred to as SD/MMC cards. Both SD and MMC cards are thin and the area they occupy is about that of a large postage stamp. Older “7-pad” MMC cards have 7 metal connector pads, while SD cards have 9 connector pads. MMC cards can fit in SD slots, but SD cards, which are packaged in about 50% thicker housings, cannot fit in MMC slots. In memory card systems that accept either SD or MMC cards, the host socket must be sized to accept both card types, and also must have an operating system capable of determining which type of card is inserted into its socket, and capable of transmitting the necessary communication protocol needed to communicate with the inserted card. When a 7-pad MMC card is inserted, only seven contact pins of the socket are used for communication, while the additional two socket pins are used when a 9-pad SD card are detected in the slot.
The 9-pad SD interface currently supports a top transfer rate of 100 Mb/s, which is sufficient for many applications. However, some applications such as storage and transport of full-motion video could benefit from higher transfer rates. One limitation to the 9-pad form factor is that data is transferred in a parallel x4-bit manner (i.e., four bits per transmission cycle).
One method to improve transmission speeds for SD and MMC cards is to facilitate x8-bit data transmission by increasing the number of contact pads to thirteen. MMC recently announced its Specification Version 4.0, which introduced a two-row, thirteen contact pad arrangement and associated electronics. While the 13-pad arrangement introduced in the MMC 4.0 specification is generally backward compatible to earlier MMC and SD cards, the arrangement calls out enlarged contact areas that preclude the formation of a write protect switch utilized in SD cards. Further, the socket proposed for use with MMC Specification Version 4.0 memory cards utilizes contact springs that are inconsistent with some contact pad locations associated with 9-pad SD memory cards. That is, while the pin configuration of the MMC 4.0 sockets allows backward compatibility with 7-pad MMC cards, it is not compatible with 9-pad Secure Digital (SD) cards. Accordingly, the MMC Specification Version 4.0 cannot be used in memory card systems that communicate with both SD and MMC card form factors, and a separate socket structure is needed to receive and read MMC and SD memory cards.
What is needed is a 13-pin memory card socket apparatus that can receive existing 7-pad MMC cards, 9-pad SD cards, 13-pad MMC devices, thereby facilitating an integrated SD/MMC system. What is also needed is a combination SD/MMC memory card that can be configured to produce any MMC or SD form factor, and can be efficiently combined with the socket apparatus to provide a low cost, highly versatile integrated SD/MMC system.